1. Field of the Invention
The present invention relates generally to the study of multiple myeloma. More specifically, the present invention relates to the identification and validation of molecular determinants of myeloma bone disease through comparative global gene expression profiling and employment of the SCID-rab mouse model for primary myeloma Further, this invention relates to methods of treatment of bone disease by stimulating bone formation and reducing bone loss via targeting molecular determinants identified by the global gene expression profiling.
2. Description of the Related Art
Multiple myeloma (MM) is a rare, yet incurable malignancy of terminally differentiated plasma cells (PC) that affects approximately 15,000 persons per year in the United States, and represents the second most common hematopoietic malignancy. Multiple myeloma represents 13% of all lymphoid malignancies in the white population and 31% of lymphoid malignancies in the black population. The malignant plasma cells home to and expand in the bone marrow causing anemia and immunosuppression due to loss of normal hematopoiesis.
Multiple myeloma is also associated with systemic osteoporosis and local bone destruction leading to debilitating bone pain and susceptibility to fractures, spinal cord compression and hypercalcemia. Myeloma is the only hematological malignancy consistently associated with lytic bone disease and local bone destruction is limited to areas adjacent to plasma cells, suggesting that the malignant plasma cells secrete factors that enhance osteoclast function and/or osteoblast anergy. The prevalence of bone disease varies with the presentation of myeloma, from smoldering myeloma, often without bone involvement, to solitary plasmacytoma, to diffused or focal multiple myeloma where systemic losses of bone mineral density or focal lytic bone lesions are seen in approximately 80% of patients.
In recent years, it has become evident that lytic bone disease is not only a consequence of myeloma, but that it is intricately involved in promoting disease progression. Change in bone turnover rates predicts clinical progression from monoclonal gammopathy of undetermined significance (MGUS) to overt myeloma by up to 3 years. While initially osteoclast and osteoblast activity are coupled, the coupling is lost with disease progression. Osteoclast activity remains increased and osteoblast activity is diminished, with lytic bone disease as the consequence. Studies in the 5T2 murine myeloma and the SCID-hu model for primary human myeloma demonstrated that inhibition of osteoclast activity is associated with inhibition of myeloma growth and reduction of myeloma tumor burden. These studies support reports that inhibition of bone resorption with bisphosphonates had an anti-myeloma effect.
Whereas the biology of osteoclasts in myeloma-associated lytic bone disease has been investigated intensively, little is known about the disease-associated changes in osteoblast activity and their underlying mechanisms. It has been suggested that in myeloma, the ability of mesenchymal stem cells to differentiate into the osteogenic lineage is impaired. However, the mechanisms responsible for such impairment have not been elucidated.
The Wnt signaling pathway is involved in both normal skeletogenesis and cancer related bone disease. The first link between Wnt signaling and human bone disease came from observations that inactivating mutations in the Wnt co-receptor, LRP5, causes the osteoporosis-pseudoglioma syndrome (OPPG). Subsequently it was shown that in the syndrome of hereditary high bone density mutations in LRP5, distinct from those seen in osteoporosis-pseudoglioma syndrome, prevent binding of Dickkopf-1 (DKK1), a soluble inhibitor of Wnt and high affinity ligand for LRP5.
The importance of DKK1 in normal skeletal development has also been demonstrated by the extra digits in DKK1 null mice and loss of bony structures in chicken and mice exposed to elevated levels of DKK1. To determine the role of DKK1 in vivo and overcome the embryonic lethality of homozygous deletion, studies have demonstrated that mice lacking a single allele of DKK1 have a marked increase in bone mass. In contrast, transgenic over-expression of DKK1 under the control of col1A1 promoters caused severe osteopenia. The osteolytic prostate cancer line PC-3, when transfected with shRNA targeting DKK1, reverted to an osteoblastic phenotype. In addition, transfection of DKK1 into the osteoblastic prostate cancer cell line C4-2B, which normally induces a mix of osteoblastic and osteolytic lesions, caused the cells to develop osteolytic tumors in SCID mice.
In addition to inhibiting osteoblastogenesis, elevated DKK1 levels may enhance osteoclastogenesis. The balance between the levels of receptor activator of the NF-kB ligand (RANKL) and osteoprotegerin (OPG), a soluble receptor and antagonist of RANK signaling, controls osteoclastogenesis in MM. Immature, but not mature, osteoblasts are rich sources of RANKL. Wnt signaling in osteoblasts up-regulates expression of OPG and down-regulates the expression of RANKL, suggesting a mechanism by which Wnt signaling in osteoblasts indirectly regulates osteoclastogenesis.
Comparative global gene expression profiling (GEP) of bone marrow plasma cells from normal healthy donors and malignant bone marrow plasma cells from newly diagnosed multiple myeloma, represents a powerful technique for identifying candidate disease genes and disrupted pathways involved in malignant transformation of multiple myeloma and multiple myeloma bone disease (Zhan et al., 2002). The prior art is deficient in such a comparative analysis to identify genes expressed in the malignant plasma cells that may be contributory to multiple myeloma bone diseases as well as aid in developing methods to diagnose and treat multiple myeloma bone diseases. Furthermore, the prior art is deficient in understanding the disease-associated changes in osteoblast activity and the underlying mechanisms in multiple myeloma associated lytic bone diseases. The present invention fulfills this longstanding need and desire in the art.